init: Start dotfiles with a test container to verify installation.

Dockerfile

@@ -0,0 +1,14 @@
+ARG BASE_REGISTRY=docker.io
+ARG BASE_IMAGE=alpine
+ARG BASE_TAG=latest
+FROM ${BASE_REGISTRY}/${BASE_IMAGE}:${BASE_TAG} AS base
+RUN apk update && \
+    apk upgrade && \
+    apk add make
+
+FROM base as test
+RUN adduser -D user
+USER user
+WORKDIR /home/user/dotfiles
+COPY --chown=user ./ ./
+ENTRYPOINT [ "make" ]